Great news - I got Vante to follow me around the house as I was clicking and giving her treats. I would walk 5-15 feet away, click, put down a treat and she ran over (EVERY TIME). The thing that really give me hope is that on the last click, Tucker started to paw at his door, she turned her head towards him, then ran over to the treat. Now that's progress.
Today, by necessity I ran across this little gem - I put them within eyesight of each other and click and give them both a treat. I did this twice and am going to remain optimistic and continue this line of good things happening in each other's presence.